A conventional drill chuck comprises a chuck body, a plurality of (for example, three) jaws, a nut, an exterior sleeve comprising a front sleeve and a rear sleeve, etc., and further comprises a bearing and a bearing washer in the case of manual locking drill chuck for reducing friction. The rear sleeve and the bearing spacer are close fitted to the chuck body, respectively. The three jaws are separately mounted in three corresponding inclined holes equally parted from each other in the chuck body. The nut is deposited in a nut slot of the chuck body, and forms a screw drive mechanism associated with the screw thread of the jaws. The nut also has a nut jacket around and closely fitted therewith. Around the nut jacket is the front sleeve that has keys in its inner wall and in the nut jacket there are recesses corresponding to the keys, such that the front sleeve can be interconnected with the nut jacket via the keys. For preventing the front sleeve from axial shifting, a buffer is close fitted in the front end of the chuck body.
In the use, one may manually rotate the front sleeve, in turn the front sleeve drives the nut jacket and the nut, and then the nut drives the jaws move forward and backward in the inclined holes of the chuck body, so that the three jaws are splayed or closed for completing the loosening and clamping of a drill tool.
However, there are some disadvantages in the prior art that the drill chuck tends to be loosening due to vibration and impact during operation, these results in that the work efficiency is badly influenced and the safety property is poor. With the broadly increasing application of the drill chuck, the request to the product in its working reliability becomes higher and higher. However, the prior art drill chuck is distinctly insufficient in performance of clamping and loosening.
Chinese patent application for invention No. 03138814.0 filed by the present inventor on Jul. 15, 2003 disclosed a locking drill chuck comprising a chuck body, a plurality of jaws, a nut, a nut jacket, a front sleeve, and a rear sleeve, wherein the chuck body has an axial hole at its rear end for engaging with a driving shaft of a driving means, and the rear sleeve close fits with the outer circumference of the rear end of the chuck body, the jaws are separately fitted in a plurality of corresponding inclined holes equally departed away from each other in the chuck body, the nut engages with the jaws, the locking drill chuck further comprises: a locking sleeve provided between the front sleeve and the rear sleeve, and connected with the front sleeve; and a locking assembly provided between the nut and a stop surface of the chuck body, the locking assembly consisting of a locking cap, rolling members, and a locking plate, wherein the locking plate has a plurality of helical grooves with helix angle in an end plane thereof, the rolling members is received in the helical grooves, the locking cap has resilient tabs securing the locking plate together with the plurality of rolling members, and the locking sleeve securely connected to the locking plate. The locking drill chuck according to said invention provides a secondary locking function through imputing torque and locking by an interlocking mechanism in addition to the first screw locking function between the nut and jaws, being reasonable in structures, easy for assembly, steady in performance, and labor saving, reliable in operating. However, such a locking drill chuck requires to machine helical grooves with helix angle, therefore, it is inconvenient for machining process, and the cost of product is high.